DECREASING PHANEROZOIC EXTINCTION INTENSITY IS A PREDICTABLE CONSEQUENCE OF EARTH SURFACE OXYGENATION AND METAZOAN ECOPHYSIOLOGY

The decline in background extinction rates of marine animals through geologic time is an established feature of the Phanerozoic fossil record. There is also growing consensus that Earth’s ocean-atmosphere system did not become oxygenated to near-modern levels until the mid-Paleozoic. Physiological theory suggests that the synergistic impacts of oxygen and temperature on aerobic respiration would have made marine animals more vulnerable to ocean warming events during periods of limited surface oxygenation. Here, we present a coupled ensemble Earth system and ecophysiological modeling approach to evaluate the feasibility of surface oxygenation as a first-order control on extinction rates through the Phanerozoic. We demonstrate that atmospheric oxygen does indeed have a fundamental influence on predicted warming-driven extinction. Although sensitivity analyses indicate that continental configuration, solar luminosity and the strength of the biological pump also impact the magnitude of modeled biodiversity loss to varying extents, atmospheric oxygen is a strong predictor of extinction vulnerability in all our analyses. We therefore suggest that the relative frequency of high-magnitude extinction events (particularly those not included in the canonical Big Five mass extinctions) early in the Phanerozoic is a predictable consequence of limited Paleozoic oxygenation and temperature-dependent hypoxia responses.